Organic electroluminescence devices (organic EL devices) are formed of fluorescent organic compounds which emit light as an electric field is applied thereto. Display devices having a display panel with each pixel being formed of an organic light emitting diode (hereinafter, an OLED) using the above-explained organic EL device are getting attention as next-generation display devices.
An organic EL device includes an anode electrode, a cathode electrode, and an organic EL layer (organic layer) which is formed between a pair of those electrodes and which includes a light emission layer, a hole-injecting layer, etc. The organic EL devices emit light using an energy generated as a hole and an electron recombine with each other in the light emission layer.
The light emission layer, the hole-injecting layer, etc., of such organic EL devices are formed by applying a liquid containing materials of the light emission layer and the hole-injecting layer to an area partitioned by a partition wall, and by letting the solvent in the liquid to dry. For application of the liquid, e.g., a nozzle-printing type application device is used.
Such an application device includes a nozzle head, and the nozzle head has a nozzle hole formed at the leading end thereof and for discharging the liquid subjected to application. As the nozzle head is pressurized, the liquid to be discharged is applied as a liquid column.
For example, Unexamined Japanese Patent Application KOKAI Publication No. 2002-75640 discloses a production method of an organic EL display device. The method uses a nozzle-printing type application device, forms a trench corresponding to a predetermined pattern where an organic EL material is to be applied on a substrate, and the substrate and a nozzle head are relatively moved so that a nozzle hole moves along the trench, thereby allowing a liquid containing the organic EL material to flow in the trench from the nozzle hole to apply such a liquid.
Meanwhile, organic EL devices have nonuniform light emission if the film thickness of the organic EL layer is nonuniform. Accordingly, in order to accomplish uniform light emission, it is necessary to control the film thickness of the organic EL layer appropriately, and to form a film having good uniformity.
According to the above-explained nozzle-printing type application device, orange of an apply area to which an apply condition adjusted so that a liquid column can be stably discharged from the nozzle hole of the nozzle head relative to an apply area with a certain size can apply appropriately is narrow, and every time the size of an apply area changes, an apply condition needs to be re-adjustment. That is, an apply condition largely changes when an organic EL material is applied to a narrow apply area in a relatively-small panel with relatively-small pixel size and with high pixel fineness and when an organic EL material is applied to a relatively-wide apply area with relatively-large pixel size and with low pixel fineness like a large-size TV.
For example, in order to increase the apply amount corresponding to a case in which a pixel is relatively large, it is an option to increase the eject speed of a liquid column by increasing liquid pressure. However, the speed for forming or maintaining a liquid column has limitations. Moreover, if the eject speed can be increased, the collision speed of a liquid against an apply area increases, resulting in splash of the liquid and spread out thereof.
Moreover, in order to increase the apply amount, it is another option to increase the size of a nozzle hole. However, as the discharge amount is proportional to the area of the nozzle hole and the nozzle area is a square of the diameter of the nozzle hole to be enlarged, a nozzle enlarging work must be highly precise. Moreover, re-adjustment of a condition of forming a liquid column becomes necessary with respect to the diameter of the nozzle hole, and the range of parameters which enables formation of respective kinds of liquid columns is not wide.
Furthermore, if the discharge amount can be increased by increasing the diameter of a nozzle hole, a liquid column formed by a discharged liquid lands on a point in an apply area, so that it is difficult to uniformly and thinly apply the liquid across a wide apply area, resulting in unevenness.